They're going down the Safari line of limiting the number of rules an extension can use, significantly reducing the efficiency of adblockers.
If it goes as planned, you won't see ads on YouTube for sure, but there likely won't be enough space to add rules for less mainstream ad networks and some of the specific sites you visit.
It's a lot more than just limiting the count; expanding the count would not offer equivalent functionality. Basically they're hobbling adblockers' ability to compete in the arms race, which makes sense as Google is an advertising company.
If it goes as planned, you won't see ads on YouTube for sure, but there likely won't be enough space to add rules for less mainstream ad networks and some of the specific sites you visit.